1. Field of the Invention
The present invention relates to a built-in antenna. The present invention in particular relates to a low profile shorted monopole antenna formed by a single metal sheet and capable of operating in the 2.4 GHz band.
2. Description of Related Art
With the development of wireless communication technology, various wireless products are widely marketed every year. Consequently related electronic circuit system and product design are focused for study and research. The mobile-unit antenna currently applied in WLAN system is a metal-plate structure or a PCB structure. The metal-plate antenna feeds RF signal by a mini-coaxial cable. On the other hand, the antenna of PCB type is almost a planar inverted-F antenna (PIFA), which is a planar antenna of inverted-F shape, and it is manufactured as a monopole antenna. The monopole antenna is constructed by a radiating unit and a grounding unit, which are separated units and do not connect with each other. An additional dielectric substrate is used for structure support for the radiating and grounding unit, and therefore the radiating rand grounding unit are printed on the dielectric substrate.
Generally speaking, the cost for manufacturing antenna of PCB type is higher than that for manufacturing the metal-plate antenna. A traditional planner monopole antenna is disclosed in Taiwan patent N.O. 00573382. The radiating unit and the grounding unit are respectively printed on two sides of a single dielectric substrate and the signals are fed in by a micro strip and a coaxial cable. According to other related patents, such as U.S. Pat. No. 6,600,448 and US 2007/0296636, the metal-plate antenna is made by molding and pressing the metal material. The two patents disclose a planar inverted-F antenna and the radiating unit and the grounding unit are formed on the same surface. Therefore, the necessary size of the antenna negatively affects the required space for the antenna, which is undesirable in this age of miniaturization.